FLOW36: A spectral solver for phase-field based multiphase turbulence simulations on heterogeneous computing architectures

We present FLOW36, a GPU-ready solver for interface-resolved simulations of multiphase turbulence. The simulation framework relies on the coupling of direct numerical simulation of turbulence, used to describe the flow field, with a phase-field method, used to describe the shape and deformation of a deformable interface and the presence of surfactants. An additional transport equation for a passive scalar can be solved to describe heat transfer in multiphase turbulence. The governing equations are solved in a cuboid domain bounded by two walls along the wall-normal direction where no-slip, free-slip or fixed/moving wall boundary conditions can be applied, while periodicity is applied along the streamwise and spanwise directions. The numerical method relies on a pseudo-spectral approach where Fourier series (periodic directions) and Chebyshev polynomials (wall-normal direction) are used to discretize the governing equations in space. Equations are advanced in time using an implicit-explicit scheme. From a computational perspective, FLOW36 relies on a multilevel parallelism. The first level of parallelism relies on the message-passing interface (MPI). A second level of parallelism uses OpenACC directives and cuFFT libraries; this second level is used to accelerate the code execution when heterogeneous computing infrastructures are targeted. In this work, we present the numerical method and we discuss the main implementation strategies, with particular reference to the MPI and OpenACC directives and code portability, performance and maintenance strategies. FLOW36 is released open source under the GPLv3 license.

本研究提出FLOW36，一款适配GPU的多相湍流界面解析数值求解器。该仿真框架耦合了用于描述流场的湍流直接数值模拟方法，与用于描述可变形界面形态、变形及表面活性剂分布的相场方法。还可通过求解被动标量输运方程，实现多相湍流中的传热过程模拟。控制方程求解于长方体计算域：沿壁面法向方向设置双侧壁面边界，可采用无滑移、自由滑移或固定/运动壁面边界条件；而沿流向与展向方向则采用周期性边界条件。数值方法采用伪谱离散格式：针对周期性方向使用傅里叶级数，针对壁面法向方向使用切比雪夫多项式，实现控制方程的空间离散。方程的时间推进采用隐式-显式分离格式。从计算架构层面来看，FLOW36采用多级并行策略：第一级并行基于消息传递接口（MPI）；第二级并行则通过OpenACC指令与cuFFT库实现，该层级可针对异构计算基础设施加速代码运行。本研究详细阐述了该数值方法，探讨了核心实现策略，重点围绕MPI与OpenACC指令的应用，以及代码的可移植性、性能优化与维护方案展开讨论。FLOW36采用GPLv3开源许可协议发布。